1. Field of the Invention
The present invention relates to a data recording method and a data recording apparatus preferably for use in a digital video tape recorder and the like, and particularly relates to a data recording method and a data recording apparatus wherein input data is subjected to error correction encoding and the error correction-encoded data is recorded on a recording medium.
2. Description of Related Art
Conventionally, a digital video tape recorder has been proposed in which every group of input video data is subjected to error correction encoding using a product code according to one or a plurality of encoding units. Thus, the error correction-encoded data in one or a plurality of encoding units is recorded on a recording medium, such as on one or a plurality of inclined tracks of a magnetic tape.
As described above, in the digital video tape recorder in which input video data is subjected to error correction encoding using a product code for each encoding unit to record the video data, portions of C2 parities, i.e., external encoding parities are respectively located and recorded on an internal portion and an end portion of each inclined track as shown in FIG. 1, for example. FIG. 1 shows an example where video data of one field is recorded on twelve inclined tracks. In this case, four tracks are simultaneously scanned by four heads at one time, and thus, all of the twelve tracks are scanned through three scanning operations.
When the data is recorded with the portions of C2 parities located at the initial and end portions of each inclined track, a sync-block, constituted by adding a C1 parity, i.e., and internal encoding parity to a data string of the C2 parity which constitutes a C1 calculation data stream, is sequentially recorded on each of the initial and end portions of each inclined track. On the other hand, a sync-block, constituted by adding a C1 parity to a data string of the video data which constitutes a C1 calculation data stream, is sequentially recorded on the center portion of each inclined track.
In this case, it is required that the calculation of the C2 parity has been completed before the portion of this C2 parity is recorded for the first time. For this reason, as a consequence, recording of data on the inclined tracks can be started only after a group of input video data is entirely captured, the C2 parity is calculated, and then the calculation of the C2 parity is completed.
For example, when a group of input video data is one field as described above, on an assumption that time T1 of one field is spent for capturing the entire group of input video data and time T2 is further spent for calculating a part of the C2 parity, the system delay Ta in an error correction code (ECC) encoder is T1+T2, which is a long system delay.
FIG. 2 shows a system delay Ta in a conventional EEC encoder. In FIG. 2, a solid line 1a shows an input processing of video data, whereas a broken line 1b shows an output processing of C2 parity and video data.
If the system delay Ta is long in the ECC encoder as described above, the time required from the initiation of the input of the input data to the initiation of the recording of this input data is also accordingly longer. As a result, the following problems arise.
1) When the video data is reproduced for confirmation immediately after the video data is recorded, the images reproduced by the reproduction video data have a large time deviation from the images produced by the input video data, which causes a user trouble in confirming the images; and
2) In order to execute a pre-read editing operation, the recording and the reproduction heads are attached at largely different heights from each other, which causes the effective track length to be shortened, resulting in deterioration in the signal to noise (S/N).
Herein, the pre-read editing operation means an editing operation in which video data of a specific frame recorded on a specific portion of a tape is reproduced, processing such as insertion of telop data into this video data of specific frame is performed, and then this video data of the specific frame is recorded again on the above-described specific portion of the tape.
FIG. 3 shows an exemplary pre-read editing system. A reproduction head Hp reproduces video data of a specific frame recorded on a specific portion of a tape 301. In this case, a reproduction amplifier 302 amplifies the reproduction signal reproduced on the reproduction head Hp, and an equalization circuit 303 has waveform-equalized the reproduction signal before a decoding circuit 304 receives it. The decoding circuit 304 decodes the waveform-equalized reproduction signal utilizing a Viterbi algorithm, for example.
An error correction code (ECC) decoder 305 receives the video data from the decoding circuit 304. The ECC decoder 305 performs error correction by use of the parities added to the video data. A video expansion circuit 306 receives the error-corrected video data from the ECC decoder 305 and expands the video data.
The video data Va output from the video expansion circuit 306 is supplied to a fixed terminal 307a of a switch circuit SW. On the other hand, telop data St to be inserted to the video data Va is supplied to a fixed terminal 307 b of the switch circuit SW, for example. In this case, the switch circuit SW is connected to the fixed terminal 307b during a period when the telop data ST is supplied, whereas the switch circuit SW is connected to the fixed terminal 307a during the other periods. Thus, the switch circuit SW outputs video data Vb into which the telop data St has been inserted.
A video compression circuit 308 then receives the video data Vb from the switch circuit SW and performs data compression thereto. In this case, for example, the video data Vb is divided into a two-dimensional blocks of 8×8 pixels, and is data-compressed by use of block encoding such as discrete cosine transform (DCT). Although not described above, the video expansion circuit 306 performs processing reversal of this data compression.
An ECC encoder 309 receives the compression-encoded data from the data compression circuit 308. The ECC encoder 309 performs error correction encoding to the compression-encoded data for each encoding unit using a product code. The video data output from the ECC encoder 309 is supplied via a recording amplifier 310 to a recording head Hr that records the reproduction signal corresponding to the video data on the portion of the tape 301 from which the reproduction head Hp has reproduced this video data.
here, during the time “t” from the point where the video data is reproduced by the reproduction head Hp to the point where the video data is recorded by the recording head Hr, the tape 301 travels a distance “d” proportional to the time “t”. For this reason, as shown in FIG. 4, the recording head Hr is attached at a position distanced from the reproduction head Hp by a difference (difference in heights between attached positions) “h” in order that, when the tape 301 travels the distance “d”, the recording head Hr scans the same portion which the reproduction head Hp scanned time “t” ago.
In this case, the recording head Hr is arranged to be in contact with the tape 301 within a range ARr. Specifically, in order to prevent the tape 301 from being cut by the recording head Hr coming into contact with the end portion of the tape 301, the recording head Hr is arranged to be in contact with the tape 301 at a position inward of the end portion of the tape 301 by a specific distance. Because of this arrangement, the reproduction head Hp comes into contact with the tape 301 within a range ARp. Therefore, this range ARp is an effective track length.
As described above, if the system delay Ta in the ECC encoder is long, the time “t” is long and the distance d is accordingly large. As a result, the step “h” is also large, resulting in a short effective track length ARp. When the effective track length ARp is short as in this case, the recording wavelength is shortened in order to ensure the same capacity of recording data as that of the case where the effective track length ARp is long. However, when the recording wavelength is short, the S/N is degraded.